Thin film magnetic disks or media are widely used as data storage media for digital computers. Typically, the disks are formed by successively sputtering onto a rigid disk substrate an underlayer, a magnetic layer and a carbon overcoat which protects the magnetic layer against wear and reduces frictional forces between the disk and the read/write head.
It is also common to lubricate the disks with a thin film of a lubricant, which is typically a fluorocarbon, such as perfluoropolyether, or a phosphazene. This lubricant layer reduces frictional interaction between the head and the disk, particularly during start/stop cycles. Typical lubricants are commercial products such as AM2001 or Z-DOL, both of which are perfluoropolyether oils. The oils are applied with a solvent so the lubricating surface will also typically contain residues of the solvent which are typically a hydrofluoroether or a hydrofluoroalkane. The lubricants may be in separate sub-layers which form the outer lubricant layer or may be present as a mixture in a single layer. The types of disks which are typically in use are thin film magnetic disks, oxide coated disks, or magneto-optical disks, all of which are referred to here as thin film disks, or simply disks.
The lubricity of disks is generally measured by a dynamic or static coefficient of friction. The dynamic friction coefficient may be measured during contact of the read/write head with a disk determined at a constant spin rate, such as 1 RPM. The static coefficient of friction may be measured using a contact start/stop (CSF) test in which the peak level of friction is measured as the disk rotates from 0 to selected RPM, such as 5000 RPM. After peak friction is been measured, the disk is brought to rest and the start/stop process is repeated for a selected number of start/stop cycles. The long term disk and drive performance requires that the disk retain a relatively low coefficient of friction after many start/stop cycles or contacts with a read/write head.
The commonly employed lubricants used on magnetic media, particularly the perfluoropolyether class of lubricants, perform well under ambient conditions but not under conditions of higher temperature and high or low humidity. Therefore, typically it is necessary to use temperature and humidity control systems to avoid less favorable environmental conditions which would otherwise cause as rapid reduction in the disk performance.